DEVELOPMENT OF THE MEMBERS OF ONE BRANCH-SYSTEM. l6l 



it is still altogether doubtful whether the branching depends, even in LycopodiacefF, on 

 true dichotomy ^ ; but the root-branches of Lycopodiacese always arise so near to 'the 

 apex, and they assume at so early a period the character of dichotomies developed in a 

 forked manner that, until further investigation proves the contrary, they must be con- 

 sidered as such. It is scarcely necessary to mention in conclusion that when roots 

 branch dichotomously the branches are at first covered by the original root-cap which 

 fills up the bifurcation, as is shown in Fig. 130. 



Fig. 130. — Dichotomy of the root of Isoetes laciistris (after 

 Hofineister) (X400); //'the apical cells of the branches; ■wh 

 the old root-cap formed before the bifurcation ; ivhl the two 

 root-caps of the branches, still covered by the former one ; e 

 epidermis ;/ parenchyma ; ryfibro-vascular bundles of the root. 



FIG. 131. — Part of a male flower of Ricinus cotnmum's 

 cut through lengthways ; // the basal portions of the 

 compouiidly branched stamens; a their anthers. 



(c) Lea'ves. Repeated bifurcations proceeding apparently from true dichotomy 

 occur in the leaves of the Fern Platyceriiim alckorne - ; and, according to an older state- 

 ment of Hofmcister, it appears that the branching of Fern-leaves generally com- 

 mences dichotomously, although mature leaves mostly resemble a monopodium. On a 

 mid-rib forming a continuation of the rachis are placed numerous alternating lobes, or 

 secondary mid-ribs with secondary lacinicP. Since these branches are apparently always 

 alternate and not opposite, and the terminal lobes of the leaves are frequently developed 

 as equally strong bifurcations, leaves of this kind may be considered, according to Hof- 

 meister's hypothesis, as dichotomies developed in a sympodial (and indeed a scorpioid) 

 manner, the mid-rib representing the sympodium and the apparent lateral branchlets the 

 weaker branches (as in Fig. 126, C); a process which is repeated in the laciniae of the leaf 

 itself when the leaf is doubly or many times pinnate. A similar interpretation may per- 

 haps be permitted for the simply pinnate leaves of Cycadese. The repeated branching 

 of the .stamens- in the male flowers of Ricinus appears, according to Payer 2, to proceed 

 from dichotomy, and to a certain extent even polytomy, commencing at an early period. 



^ Compare Nageli's Beitrage zur wissen. Botanik, Heft IV. 1867. I would lay less stress on the 

 relation of dichotomies to the apical cell, because the latter has scarcely the same decided signifi- 

 cation in LycopodiaceK as in Ferns, Equisetaceae, and other Cryptogams ; and the apical growth 

 apparently approaches nearer to that of Phanerogams. 



2 The leaf-stalk oi Adiantum pedatum divides above into two equally strong branches, each of 

 which forms a helicoid cyme of ramifications evidently arising by dichotomy ; the weaker branches 

 of the helicoid cyme stand upright and form each a mid-rib with numerous pinnate leaflets ; and 

 thus probably a scorpioid cyme produced by further dichotomy. This is one of the most beautiful 

 forms of leaves, the history of the development of which would be of unusual interest. 



' Payer, Organogenic de la fleur, pi. 108. 



M 



